Contingency analysis of presence/absence of metal grating and penetration resistance (frequencies per class).
| Sampling zone | Metal grating | Penetration resistance | Pearson χ2 statistic | |||
|---|---|---|---|---|---|---|
| Class 1 | Class 2 | Class 3 | Class 4 | |||
| Surface level | Absence | 29% | 26% | 22% | 23% | 10.26z |
| Presence | 36% | 25% | 13% | 26% | ||
| 15 cm depth (5.9 in) | Absence | 7% | 16% | 15% | 62% | 3.45z |
| Presence | 11% | 15% | 16% | 58% | ||
| 30 cm depth (11.8 in) | Absence | 2% | 8% | 12% | 78% | 7.26z |
| Presence | 6% | 8% | 15% | 71% | ||
| 45 cm depth (17.7 in) | Absence | 2% | 3% | 6% | 89% | 9.59z |
| Presence | 3% | 4% | 7% | 86% | ||
↵z Ho: independence of variables not rejected (significance level α is > 0.01).